1. Field of the Invention
This invention refers to a switch control mechanism comprising a locking clamp being shiftable by means of a push rod and having on its end facing the switch tongue or the like a swivel head being swivelably connected with the switch tongue and comprising at its other end a locking clamp head cooperating with a locking piece, noting that a shoulder of the locking clamp head contacts in the locked position a shoulder of the locking piece and noting that the switch tongue rail is linked to the swivel head of the locking clamp with interposition of a pin arranged within an elongated slot extending in the longitudinal direction of the tongue rail. It is in particular on occasion of extreme temperature conditions that a longitudinal extension of the switch tongue takes place, which may give rise to jamming of the push rod and of the locking clamp within the locking piece if the switch tongue is rigidly linked to the swivel head. On account of the pin, with interposition of which the switch tongue is linked to the swivel head, engaging an elongated slot of the switch tongue extending in the longitudinal direction of the switch tongue, such longitudinal expansions of the switch tongue are compensated and neutralized.
2. Description of the Prior Art
Such an arrangement has become known from AT-PS No. 250 433. In this case, the pin is engaging an elongated slot provided in the rail foot of the tongue rail. The disadvantage of this arrangement is that the tongue rail is weakened by this elongated slot and there exists the risk of fracture. From AT-PS No. 382 128 there has become known an arrangement in which the locking piece is connected with the stock rail for being shiftable in longitudinal direction of the rail and thus for accommodating a longitudinal expansion of the tongue rail. In this arrangement, the swivel head of the locking clamp is rigidly linked to the tongue rail, so that weakening of the tongue rail on account of elongated slots provided in the rail foot is avoided. The bearing means of the pin for linking the swivel head is connected with the locking piece via a rod structure, and in case of a longitudinal expansion of the switch tongue, the locking piece is thus shifted along the stock rail, so that the relative position of the locking piece with respect to the swivel point of the tongue rail on the swivel head remains unchanged. In this case, there must be provided sliding surfaces for the locking piece and in case of lacking permanent servicing of these sliding surfaces friction of these sliding surfaces is possible and jamming may again occur. Such an arrangement is relatively complicated and expensive and also offers no complete safety against jamming, because the locking piece must be taken along on occasion of longitudinal expansions of the tongue rail and jamming may already occur if taking along is effected by the rod structure. In the embodiment, in which linking of the tongue rail to the swivel head of the locking clamp is effected via an elongated slot, longitudinal expansions of the tongue rail are, however, directly compensated at the location of its origin.